Software Flow Control - PictureTel Concorde 4500 Servicing Manual

CONTROL AND DATA PORT COMMUNICATIONS

Software Flow Control

D-8
Table D-2: Modem Control Signals
Signal
DTR Data Terminal Ready. The terminal device asserts
the DTR signal to indicate that data can be accepted.
The terminal device deasserts the DTR signal to
indicate that it cannot accept data.
DSR Data Set Ready. The Concorde¥4500 sends the DSR
signal to acknowledge the DTR signal from the
terminal device.
RTS Request to Send. The terminal device asserts the
RTS signal when it is ready to send data to the
Concorde¥4500. If the Concorde¥4500 is able to
receive the data, it responds by raising the CTS
signal; the terminal device is now free to send the
data to the Concorde¥4500.
CTS Clear to Send. The Concorde¥4500 uses the CTS
signal to control the ßow of data from the terminal
device. The Concorde¥4500 asserts this signal to
start data ßow and deasserts this signal to stop the
ßow. The Concorde¥4500 must Þrst receive an
asserted RTS signal from the terminal device. After
receiving this signal, the Concorde¥4500 asserts the
CTS signal. Data being transmitted while the CTS
signal is deasserted is buffered; if the buffer
overßows, the data is lost.
The Concorde¥4500 always uses the CTS method of
ßow control, regardless of whether the DTE uses or
ignores this signal.
Software ßow control is used only in asynchronous communication.
Control port B on the back of the DI board uses asynchronous
control to transmit data. Software ßow control uses American
Standard Code for Information Interchange (ASCII) codes to stop
and start the ßow of data.
Description